U.S. patent number 4,161,235 [Application Number 05/907,523] was granted by the patent office on 1979-07-17 for elevator system.
This patent grant is currently assigned to Westinghouse Electric Corp.. Invention is credited to William R. Caputo, Alan L. Husson.
United States Patent |
4,161,235 |
Caputo , et al. |
July 17, 1979 |
Elevator system
Abstract
An elevator system in which the movement of the elevator car is
responsive to a comparator which provides an error signal
responsive to the difference between the magnitude of a speed
pattern signal provided by a speed pattern generator, and a signal
responsive to actual car speed. An adjustable impedance device
controls the affect of the speed pattern signal on the comparator,
with the impedance of the adjustable impedance device being
responsive to at least one predetermined parameter of the speed
pattern signal.
Inventors: |
Caputo; William R. (Wyckoff,
NJ), Husson; Alan L. (Hackettstown, NJ) |
Assignee: |
Westinghouse Electric Corp.
(Pittsburgh, PA)
|
Family
ID: |
25424253 |
Appl.
No.: |
05/907,523 |
Filed: |
May 19, 1978 |
Current U.S.
Class: |
187/293 |
Current CPC
Class: |
H02P
7/293 (20160201); B66B 5/10 (20130101) |
Current International
Class: |
B66B
5/08 (20060101); B66B 5/10 (20060101); H02P
7/292 (20060101); H02P 7/18 (20060101); B66B
001/30 () |
Field of
Search: |
;187/29 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Truhe; J. V.
Assistant Examiner: Duncanson, Jr.; W. E.
Attorney, Agent or Firm: Lackey; D. R.
Claims
We claim as our invention:
1. An elevator system, comprising:
an elevator car,
motive means for said elevator car,
speed pattern means providing a speed pattern signal indicative of
the desired speed of said elevator car,
means providing a velocity signal responsive to the actual speed of
said elevator car,
controllable impedance means,
control means providing a first control signal responsive to at
least one predetermined parameter of said speed pattern signal,
said control means including reference means providing a first
reference signal relative to said at least one predetermined
parameter, said control means modifying the impedance of said
controllable impedance means in response to a predetermined
relationship between said first control signal and said first
reference signal,
and error signal means providing an error signal for controlling
said motive means in response to said velocity signal and said
speed pattern signal,
said controllable impedance means being connected to modify the
affect of said speed pattern signal on said error signal means, at
least when its impedance is modified by said control means.
2. The elevator system of claim 1 wherein the control means
additionally provides a second control signal responsive to at
least one predetermined parameter of the velocity signal, with the
reference means providing a second reference signal relative to
said at least one predetermined parameter of the velocity signal,
and wherein the control means modifies the impedance of the
controllable impedance means in response to a predetermined
relationship between said second control signal and said second
reference means.
3. The elevator system of claim 1 wherein the speed pattern signal
provided by the speed pattern means has different polarities for
the up and down travel directions, and wherein the first control
signal is a single polarity signal.
4. The elevator system of claim 1 wherein the controllable
impedance means is connected to have the affect on the error signal
means of pulling the magnitude of the speed pattern signal towards
ground, regardless of the polarity of the speed pattern signal.
5. The elevator system of claim 1 wherein the at least one
predetermined parameter of the speed pattern signal is the
magnitude of the speed pattern signal, the first reference signal
is the desired maximum value of the speed pattern signal, and the
predetermined relationship which causes the control means to modify
the impedance of the controllable impedance means is the magnitude
of the first control signal exceeding the magnitude of the first
reference signal.
6. The elevator system of claim 5 wherein the control means reduces
the impedance of the controllable impedance means when the
magnitude of the first control signal exceeds the magnitude of the
first reference signal, until the magnitude of the speed pattern
signal drops below the magnitude of the first reference signal.
7. The elevator system of claim 1 wherein the first control signal
is responsive to at least one predetermined parameter of the speed
pattern signal, and to an additional parameter, with the at least
one parameter being the magnitude of the speed pattern signal, and
with the additional parameter being a factor related to the rate of
change of the speed pattern signal, and wherein the predetermined
reference signal is the desired maximum value of the speed pattern
signal, and wherein the predetermined relationship therebetween
which causes the control means to modify the impedance of the
controllable impedance means is the magnitude of the first control
signal exceeding the magnitude of the first reference signal,
whereby the elevator car attains the maximum desired speed without
overshoot.
8. The elevator system of claim 1 wherein the at least one
predetermined parameter of the speed pattern signal is the rate of
change of the speed pattern signal, the first reference signal is
the desired maximum value of the rate of change of the speed
pattern signal, and the predetermined relationship which causes the
control means to modify the impedance of the controllable impedance
means is the magnitude of the first control signal exceeding the
magnitude of the first reference signal.
9. The elevator system of claim 8 wherein the control means reduces
the impedance of the controllable impedance means, when the
magnitude of the rate of change of the speed pattern signal exceeds
the magnitude of the first reference signal, until the magnitude of
the rate of change of the speed pattern signal drops below the
magnitude of the first reference signal.
10. The elevator system of claim 1 wherein the at least one
predetermined parameter of the speed pattern signal is the rate of
change of the speed pattern signal, the first reference signal is
the desired maximum value of the rate of change of the speed
pattern signal, and wherein the control means additionally provides
a second control signal responsive to the magnitude of the speed
pattern signal, and the reference means provides a second reference
signal representative of the desired maximum value of the speed
pattern signal, with the control means modifying the impedance of
the controllable impedance means in response to a predetermined
relationship between the magnitude of the second control signal,
and the magnitude of the second reference signal.
11. The elevator system of claim 10 wherein the second control
signal, in addition to a factor representative of the desired
maximum value of the speed pattern signal, includes a factor
responsive to the rate of change of the speed pattern signal.
12. The elevator sytem of claim 1 wherein the controllable
impedance means is a field effect transistor having main and gate
electrodes, with its gate electrode being connected to the control
means, and with its main electrodes providing a path to ground for
the speed pattern generator signal at a point between the speed
pattern means and error signal means.
13. The elevator system of claim 1 wherein the speed pattern signal
has different polarities for the up and down travel directions of
the elevator car, and wherein the control means includes absolute
value means which provides a single polarity signal responsive to
the absolute value of each polarity of the speed pattern signal,
and including slope limiting means for limiting the rate of change
of the speed pattern signal prior to the processing of the speed
pattern signal by the control means, preventing the speed pattern
signal from rapidly changing from its maximum value at one polarity
to its maximum value at the other polarity, enabling the absolute
value means to detect such a change.
14. An elevator system, comprising:
an elevator car,
motive means for said elevator car,
speed pattern means providing a speed pattern signal indicative of
the desired speed of said elevator car,
means providing a velocity signal responsive to the actual speed of
said elevator car,
controllable impedance means,
absolute value means providing a single polarity absolute value
signal responsive to the absolute value of said speed pattern
signal,
control means providing a first control signal responsive to the
magnitude of the absolute value signal, and a second control signal
responsive to the rate of change of the absolute value signal,
reference means providing first and second reference signals
responsive to desired maximum values for the magnitude of the
absolute value signal, and the rate of change of the absolute value
signal, respectively,
first comparator means providing a first modification signal which
modifies the impedance of said controllable impedance means when
the first control signal exceeds the first reference signal,
second comparator means providing a second modification signal
which modifies the impedance of said controllable impedance means
when the second control signal exceeds the second reference
signal,
and error signal means providing an error signal for controlling
said motive means in response to said velocity signal and said
speed pattern signal,
said controllable impedance means being connected to modify the
effect of said speed pattern signal on said error signal means, at
least when its impedance is modified by at least one of the first
and second comparator means.
15. The elevator system of claim 14 including slope limiting means,
said slope limiting means limiting the rate of change of the speed
pattern signal, with the control means being responsive to the
speed pattern signal after the speed pattern signal has been
monitored and limited by said slope limiting means.
16. The elevator system of claim 14 wherein the control means
includes means for additionally making the first control signal
responsive to a factor related to the rate of change of the
absolute value signal, to cause the elevator car to approach the
maximum speed dictated by the speed pattern signal without
overshoot thereof.
17. An elevator system, comprising:
an elevator car,
motive means for said elevator car,
speed pattern means providing a speed pattern signal indicative of
the desired speed of said elevator car,
means providing a velocity signal responsive to the actual speed of
said elevator car,
controllable impedance means,
control means providing a first control signal responsive to at
least one predetermined parameter of said velocity signal, said
control means including reference means providing a first reference
signal relative to said at least one predetermined parameter, said
control means modifying the impedance of said controllable
impedance means in response to a predetermined relationship between
said first control signal and said first reference signal,
and error signal means providing an error signal for controlling
said motive means in response to said velocity signal and said
speed pattern signal,
said controllable impedance means being connected to modify the
affect of the speed pattern signal on said error signal means, at
least when its impedance is modified by said control means.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates in general to elevator systems, and more
specifically to elevator systems of the type which are controlled
by a speed pattern generator.
2. Description of the Prior Art
It is conventional in traction elevator systems of the type in
which the elevator car is responsive to a drive machine which
includes a D.C. motor, to control the speed of the D.C. motor, and
thus the speed of the elevator car, in response to the error or
deviation between a speed pattern signal provided by a speed
pattern generator, and a signal responsive to the actual speed of
the elevator car.
Predetermined failure modes of the speed pattern generator may
result in the elevator car exceeding its rated maximum speed. At a
first overspeed magnitude, the governor speed reducing switch
operates to reduce the magnitude of the speed pattern signal. At a
second overspeed magnitude, an emergency stop is made. If the
elevator car reaches a third overspeed magnitude, the safety is
set. Thus, it would be desirable to monitor predetermined
parameters of the speed pattern signal, such as the magnitude of
the speed pattern signal, and the rate of change of the speed
pattern signal, before it is applied to the comparator which
generates the error signal, and to modify the affect of the speed
pattern signal on the comparator when either its magnitude, or its
rate of change, or both, exceed predetermined values. Monitoring of
the speed pattern signal, and limiting predetermined parameters
thereof, however, must be accomplished by monitoring and limiting
circuits which have no failure modes which could result in a car
overspeed condition.
Further, it would be desirable for the elevator car to approach its
rated maximum speed without overshoot, as the speed governor trip
settings may be made closer to the maximum rated speed without
nuisance trips, when overshooting is not present. Such overshoot of
maximum rated speed may be prevented by adjusting the dynamics of
the traction drive machine. However, this may be undesirable as it
may result in sluggishness of the elevator car during landings.
Thus, it would be desirable to be able to prevent overshoot of the
maximum car speed, without changing the dynamics of the motor
drive, or otherwise deleteriously affecting the performance of the
elevator system.
SUMMARY OF THE INVENTION
Briefly, the present invention is a new and improved elevator
system of the traction type which includes an elevator car, a drive
machine for the elevator car, a speed pattern generator providing a
speed pattern signal, a device for providing a velocity signal
responsive to the actual speed of the elevator car, and error
signal means providing an error signal for controlling the drive
machine in response to the deviation of the velocity signal from
the speed pattern signal. A controllable impedance device, such as
a field effect transistor, is connected such that when it is
conductive it pulls the speed pattern signal toward ground,
regardless of the polarity of the speed pattern signal. No failure
modes of the field effect transistor, when it is connected to pull
the speed pattern signal towards ground, can result in increasing
the speed of the elevator car. The impedance of the controllable
impedance device is responsive to control circuitry which processes
the speed pattern signal to obtain control signals responsive to
the parameters to be monitored and limited. Comparators compare the
control signals with appropriate reference signals, and they
provide signals which modify the impedance of the controllable
impedance device when the reference signals are exceeded.
In a preferred embodiment of the invention, a control signal
responsive to the maximum desired value of the speed pattern signal
includes a factor related to the rate of change of the speed
pattern signal. By comparing this control signal with a reference
related to maximum car speed, the car approaches the maximum car
speed smoothly and exponentially, without overshoot.
Slope limiting means is applied to the speed pattern signal prior
to the processing of the speed pattern signal by the monitoring and
limiting means, permitting the use of absolute value circuitry in
the monitoring and limiting functions.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention may be better understood, and further advantages and
uses thereof more readily apparent, when considered in view of the
following detailed description of exemplary embodiments, taken with
the accompanying drawings, in which:
FIG. 1 is a partially schematic and partially block diagram of an
elevator system constructed according to the teachings of the
invention;
FIG. 2 is a schematic diagram illustrating an exemplary
implementation of certain of the functions shown in block form in
FIG. 1; and
FIG. 3 is a graph which illustrates car response to a stepped speed
pattern signal, as various features of the invention are added to
the monitoring and limiting circuitry.
DESCRIPTION OF PREFERRED EMBODIMENTS
Referring now to the drawings, and FIG. 1 in particular, there is
shown a partially schematic and partially diagrammatic view of an
elevator system 10 constructed according to the teachings of the
invention. Elevator system 10 includes a direct current drive motor
12 having an armature 14 and a field winding 16. The armature 14 is
electrically connected to an adjustable source of direct current
potential. The source of potential may be a direct current
generator of a motor-generator set in which the field current of
the generator is controlled to provide the desired magnitude and
polarity of unidirectional potential; or, as shown in FIG. 1, the
source of direct current potential may be a static source, such as
a dual converter 18.
As is well known in the art, the dual converter 18 includes first
and second converter banks which may be three-phase, full-wave
bridge rectifiers connected in parallel opposition. Each converter
includes a plurality of static controlled rectifier devices
connected to interchange electrical power between alternating and
direct current circuits. The alternating current circuit includes a
source 22 of alternating potential and busses 24, 26 and 28; and,
the direct current circuit includes busses 30 and 32, to which the
armature 14 of the direct current motor 12 is connected. The dual
bridge converter 18 not only enables the magnitude of the direct
current voltage applied to the armature 14 to be adjusted, by
controlling the conduction or firing angle of the controlled
rectifier devices, but it allows the direction of the direct
current flow through the armature to be reversed when desired, by
selectively operating the converter banks. Dual converter apparatus
which may be used is shown in detail in U.S. Pat. Nos. 3,713,011
and 3,713,012, which are assigned to the same assignee as the
present application.
The field winding 16 of drive motor 14 is connected to a source 34
of direct current voltage, represented by a battery in FIG. 1, but
any suitable source, such as a single bridge converter, may be
used.
The drive motor 12 includes a drive shaft indicated generally by
broken line 36, to which a traction sheave 38 is secured. An
elevator car 40 is supported by wire ropes 42 which are reeved over
the traction sheave 38, with the other ends of the ropes being
connected to a counterweight 44. The elevator car is disposed in a
hoistway 46 of a structure having a plurality of floors or
landings, such as floor 48, which are served by the elevator car. A
tachometer 52 provides a signal VT1 responsive to the actual speed
of the elevator car.
The movement mode of the elevator car 40 and its position in the
hoistway 46 are controlled by the voltage magnitude applied to the
armature 14 of the drive motor 12. The magnitude of the direct
current voltage applied to armature 14 is responsive to a speed
pattern signal or velocity command signal VSP provided by a
suitable speed pattern generator 50. For example, the speed pattern
generator may be constructed as disclosed in U.S. Pat. No.
3,774,729, which is assigned to the same assignee as the present
application. A servo control loop 51 controls the speed of the
drive motor, and thus the position of the elevator car 40 in
response to the velocity command signal VSP. Any suitable servo
control loop may be used, such as the control loop disclosed in the
hereinbefore mentioned U.S. Patents, as well as improvements
thereon, such as disclosed in U.S. Pat. No. 4,030,570, which is
assigned to the same assignee as the present application.
For purposes of describing the present invention, the control loop
51 is illustrated as being responsive to supervisory control 129,
which receives calls for elevator service and signals responsive to
the location and travel direction of the elevator car 40. In
response to these calls and signals, the supervisory control
provides signals for controlling the speed pattern generator 50 to
initiate the acceleration and deceleration portions of the speed
pattern signal VSP as required to serve the calls for elevator
service. Suitable supervisory control is disclosed in the
hereinbefore mentioned U.S. Pat. No. 3,774,729.
In a conventional or prior art control loop the output signal VSP
of the speed pattern generator, representing the desired elevator
car, and the velocity feedback signal VT1, which represents the
actual speed of the elevator car, would be applied to a summing
point to provide a difference signal which would be applied to an
error amplifier 54. The amplified error signal VE would be
additionally processed in feedback control, shown generally at 56,
with such feedback, for example, including a current signal from
current transformers 84, and a velocity signal VT1 which may be
differentiated to obtain an acceleration signal for stabilization
purposes. The feedback circuits are described in the hereinbefore
mentioned U.S. patents. The additional feedback control 56 provides
a control signal VC for a phase controller 90, which receives
waveform information from A.C. conductors 24, 26 and 28, and it
provides firing pulses for the controllable switching devices of
the dual bridge converter 18. A suitable phase controller is
illustrated in the hereinbefore mentioned U.S. Pat. Nos. 3,713,011
and 3,713,012.
The present invention relates to the monitoring and limiting of
certain parameters of the speed pattern signal VSP. The speed
pattern signal VSP is of one polarity when the elevator car is to
go in the up direction, and of the opposite polarity when it is to
go in the down direction. Thus, it would be convenient in the
monitoring circuits to obtain a single polarity signal responsive
to the absolute value of the speed pattern signal, and to process
this single polarity signal, regardless of the instant polarity of
the speed pattern signal VSP. A malfunction in the speed pattern
generator which would instantaneously switch the pattern from
maximum rated speed in one direction, to maximum rated speed in the
other direction, would not be detected when using absolute value
processing circuitry. Thus, the elevator car could be subjected to
an excessive rate of deceleration, and acceleration, even with
acceleration limiting features in the monitoring and limiting
circuitry. This can be prevented by processing the positive speed
pattern signal with one set of monitoring and limiting circuitry,
and the negative speed pattern signal with another set of
monitoring and limiting circuitry. However, in a preferred
embodiment of the invention, the necessity of two complete sets of
monitoring and limiting circuitry is eliminated, and absolute value
processing of the speed pattern signal is made practical, by
applying the speed pattern signal VSP to a slope limiting function
58. The slope limiting function 58 prevents any quick change in the
speed pattern signal, limiting the maximum rate of change thereof
to a corresponding maximum acceleration and deceleration, which may
be 7 feet/second.sup.2, for example. The slope limiting function
enables the monitoring and limiting functions, which are located
further downstream in the control loop, to handle pattern reversal,
or failure of the speed pattern generator, i.e., pattern drop-out.
The slope limiting function 58 limits the rate of change of the
speed pattern signal to a value which can be adequately monitored
by the monitoring and limiting functions of the invention. The
slope limited speed pattern signal is referenced VSP', in order to
indicate that it has been processed by the slope limiting
function.
It is of the utmost importance that the monitoring and limiting
functions be fail-safe, from the standpoint of not adding any
failure modes which could result in increasing the magnitude of the
speed pattern signal, and thus increasing the speed of the elevator
car. The present invention is fail-safe in that the sole affect on
the speed pattern signal VSP' which can possibly be provided by the
monitoring and limiting circuits is to pull the speed pattern
signal VSP towards ground, thus reducing, instead of increasing,
the speed requested by the speed pattern generator.
More specifically, the usual summing resistor for the speed pattern
signal VSP is divided into two serially connected resistors 60 and
62, each equal to one-half of the value of the usual summing
resistor. For example, each may be 10K ohms. The junction 64
between resistors 60 and 62 is connected to ground 66 via a
controllable impedance device 68. In a preferred embodiment, the
controllable impedance device is a field effect transistor, because
of its high input impedance, and because it is voltage controlled,
requiring an almost insignificant gate current. A specific
embodiment of the invention using a field effect transistor will be
described in detail with reference to FIG. 2.
The controllable impedance device 68 is controlled by a monitoring
and limiting function 72, which monitors the speed pattern signal
VSP' at junction 64. Junction 64 is also connected to a positive
source of potential, such as +15 volts, via a resistor 74. Resistor
74 has a large value, such as 4.7 megohms, which is selected to
cancel the small amount of biasing current drawn by the monitoring
and limiting functions. The biasing current, while small, could
result in a positional error at low car speeds, without the
offsetting compensation provided by resistor 74 and the positive
source of potential.
While the monitoring and limiting of the speed pattern signal VSP'
may be solely responsive to parameters of the speed pattern signal
itself, the monitoring and limiting of the speed pattern signal may
also be responsive to one or more predetermined parameters of the
actual speed of the elevator car, as represented by velocity signal
VT1. Thus, signal VT1 is illustrated in FIG. 1 as also being
connected to the monitoring and limiting function 72.
The velocity signal VT1 is applied to an input of error amplifier
54 via a resistor 76. Error amplifier 54 may be an operational
amplifier (op amp) 78 having a feedback resistor 80. Resistors 62
and 76 are connected to the inverting input of op amp 78, and the
non-inverting input is connected to ground. The remaining portions
of the control loop 51 may be as described in the hereinbefore
mentioned U.S. patents.
In the operation of the elevator system 10 the controllable
impedance device 68 is biased to its non-conductive state. The
monitoring and limiting function 72 is designed with a high input
impedance and thus does not load the control loop. Thus, when the
speed pattern signal VSP' and the velocity signal VT1 are not
exceeding any of the preset limits for the monitored parameters,
the monitoring and limiting function 72 has no affect on the speed
pattern signal. In a preferred embodiment of the invention, a
factor related to the rate of change of the speed pattern, and also
of the actual car speed, if desired, is introduced into a limiting
function related to the maxium rated car speed. This
interrelationship between speed, and the rate of change of speed,
results in the elevator car entering the maximum speed phase of its
run smoothly and exponentially, without overshoot. Thus, in this
embodiment, the monitoring and limiting function modifies the
affect of the speed pattern signal on the error amplifier 54 on
every run of the elevator car during which the maximum rated speed
of the elevator car is attained.
The monitoring and limiting function 72 modifies the affect of the
speed pattern signal on the error amplifier by reducing the
impedance of the controllable impedance device 68 by a controlled
magnitude, which results in pulling the speed pattern signal closer
to ground, regardless of the polarity of the speed pattern signal.
The impedance of the controllable impedance device 68 is reduced to
the point necessary to bring the speed pattern signal within the
preset limits established for the speed pattern signal, and also
for the velocity signal VT1, if the velocity signal VT1 is also
monitored.
FIG. 2 is a schematic diagram of circuitry which may be used to
perform certain of the functions shown in block form in FIG. 1. The
slope limiting function 58 may be provided by first and second op
amps 100 and 102, respectively, with the first op amp 100 being
connected as a high gain linear amplifier, and the second connected
as an integrator. The signal VSP is applied to the inverting input
of op amp 100 via a resistor 103, with negative feedback being
provided via a resistor 105. The output of op amp 100 is applied to
the inverting input of op amp 102 via a resistor 107, and the
non-inverting input of op amp 102 is tied to ground via a resistor
109. An RC circuit including capacitor 111 and resistor 113 is
connected from the output of op amp 102 to ground, with a junction
between capacitor 111 and resistor 113 being connected to the
inverting input of op amp 102. The output of op amp 102 is also
connected to the non-inverting input of op amp 100 via a resistor
115. The double inversion provided by this circuit, with the output
of op amp 102 being fed back to the non-inverting input of op amp
100, results in the output of op amp 102 following the polarity of
the input. The output faithfully follows the input, except for a
rapid change in the input voltage. The response time for a rapid or
step change is selected such that the maximum rate of change of the
output for a step input is equivalent to the maximum desired
acceleration, or deceleration rate, such as 7 feet/second.sup.2,
for example.
The speed pattern signal appearing at junction 64 is applied to the
controllable impedance device 68, which includes an N-channel,
junction field effect transistor (JFET) 104. JFET 104 is connected
to function as a voltage variable resistor in which the
drain-to-source resistance of the device is controlled by the bias
voltage between the gate and source. A bias resistor 106 is
connected from an input terminal 108 to the source S, and the
source S is connected to ground 66. Input terminal 108 is connected
to gate G via a resistor 110, and a resistor 112 is connected from
the drain D to the gate G. Junction 64 is connected to the drain D.
Resistors 110 and 112 are selected to have very large values, such
as 1.5 megohms and 3 megohms, respectively. Thus, any short circuit
failure modes of FET 104 will not cause the control voltage at
input terminal 108 to have any appreciable affect on the voltage at
junction 64.
The control voltage at input terminal 108 is provided by the
monitoring and limiting function 72. The monitoring and limiting
function 72 is responsive tothe pattern voltage at junction 64,
and, if desired, it may also be responsive to the velocity signal
VT1. The monitoring and limiting function will only be described in
detail relative to the processing of the speed pattern signal VSP',
as similar circuitry may be used to process the velocity signal
VT1.
More specifically, the speed pattern signal VSP' is first applied
to an input buffer and absolute value function 114. This function
includes first, second, and third op amps 116, 118 and 120,
respectively. Op amp 116 is connected as a non-inverting amplifier
to function as a high input impedance follower, op amp 118 is
connected as a precision rectifier, and op amp 120 is connected as
a summing amplifier. Op amps 118 and 120 provide a precision
full-wave rectification of the input signal, with the output of op
amp 120 being negative, regardless of the polarity of the input
signal.
More specifically, the speed pattern signal VSP' is applied to the
non-inverting input of op amp 116, and the output of op amp 116 is
fed back to its inverting input via a resistor 117. The output of
op amp 116 is applied to the inverting input of op amp 118 via a
resistor 119, and the non-inverting input of op amp 118 is
connected to ground via a resistor 121. The inverting input of op
amp 118 is connected to the inverting input of op amp 120 via
serially connected diodes 123 and 125 and a resistor 131. The
output of op amp 118 is connected to the junction between diodes
123 and 125, and a resistor 127 is connected across the serially
connected diodes 123 and 125. The output of op amp 116 is also
connected to the inverting input of op amp 120 via a resistor 133.
The non-inverting input of op amp 120 is connected to ground via a
resistor 135. Negative feedback for op amp 120 is provided via a
resistor 137.
The first parameter of the speed pattern signal which is monitored
is the rate of change of the pattern signal, i.e., acceleration. An
acceleration monitoring function 122 includes an op amp 124
connected as a differentiator. The output of op amp 120 is applied
to the inverting input of op amp 124 via serially connected
capacitor 139 and resistor 141. The non-inverting input of op amp
124 is tied to ground via a resistor 143. Resistors 145 and 147 are
connected from the output of op amp 124 to ground, and the junction
between these resistors is connected to the inverting input of op
amp 124. Since noise is introduced with any differentiating step, a
filter capacitor 149 may be connected across the negative feedback
resistor 145, as shown.
The output of op amp 124 is a positive signal having a magnitude
responsive to the rate of change of the speed pattern signal VSP'.
This output signal is applied to a comparator 126, which may
include an op amp 128. The output of op amp 124 is applied to the
non-inverting input of op amp 128 via a resistor 151, and a
positive reference voltage is applied to the inverting input of op
amp 128 via an adjustable resistor 153 and a fixed resistor 155.
The adjustable resistor 153 is connected from a positive source of
potential, such as +15 volts, to ground, and the inverting input of
op amp 128 is connected to the adjustable arm of resistor 153 via
the fixed resistor 155. The positive reference voltage is selected
such that the acceleration limit has the desired value, such as
about 1.1 times the normal acceleration rate. A capacitor 157 may
be connected from the output of op amp 128 to the inverting input
thereof, in order to remove a sawtooth ripple from the output of op
amp 128.
As long as the input voltage to the non-inverting input of op amp
128 is less than the reference voltage, the output of op amp 128
will be negative. When the output from the acceleration circuit 122
exceeds the reference, the output of op amp 128 will switch to a
positive polarity.
A biasing and clamp circuit for JFET 104 includes a junction 130 to
which input terminal 108 of a controllable impedance device 68 is
connected via a diode 132. Diode 132 is poled to prevent the
gate-source of JFET 104 from being forward biased. Forward biasing
is to be avoided, as it would destroy the high input impedance of
the JFET, and cause gate current to flow which would load down the
speed pattern circuit.
Negative bias for JFET 104 is provided by a source of negative
potential, such as -15 volts which source is connected to junction
130 via a resistor 134. The negative bias is selected to pinch-off
drain-source current flow through JFET 104. The output of op amp
128 is connected to junction 130 via a diode 159. Diode 159 is
poled to conduct current toward junction 130.
When the output of comparator 126 switches positive, indicating
acceleration limiting is necessary, junction 130 becomes less
negative, and the drain-source resistance of JFET 104 is reduced
accordingly, allowing current flow therethrough. If the pattern
signal has a positive polarity at this time, current flows away
from junction 64 to pull the pattern towards ground. If the pattern
signal has a negative polarity at this time, current flows towards
junction 64, which also pulls the speed pattern signal back towards
ground.
Another parameter of the speed pattern signal VSP' which is
monitored, is the maximum value of the pattern signal. This
monitoring function is accomplished by the circuit 136. Circuit 136
includes an op amp 140. The value of the speed pattern signal at
any instant is applied to the inverting input of op amp 140 via a
resistor 142. If it is only desirable to monitor maximum speed,
this input would be sufficient. In a preferred embodiment of the
invention, it is also desirable to anticipate the arrival of the
speed pattern at the maximum speed point, and to take any
corrective action which is necessary to enable the elevator car to
smoothly and exponentially blend into the maximum speed, without
overshoot. This is accomplished by adding to the inverting input of
op amp 140 a signal related to the rate of change of a speed
pattern signal, with a capacitor 144 and a resistor 146 being
connected from the output of op amp 120 to the inverting input of
op amp 140. Thus, when the speed pattern signal is in its
acceleration phase, a signal responsive to the value of the speed
pattern signal, plus a factor related to acceleration, provides a
signal at the inverting input of op amp 140 which will be more
negative than it would otherwise be when using merely the value of
the speed pattern signal. This in turn provides a signal at the
output of op amp 140 which is more positive than it would otherwise
be, in order to indicate to the following comparator circuit that
the speed pattern has reached its maximum value, when it actually
has not attained that value. As illustrated, a filter capacitor 148
may be connected across the negative feedback resistor 150, for
reducing electrical noise.
The output of op amp 140 is applied to a comparator 152 which is
similar in construction to comparator 126. Comparator 152 includes
an op amp 154 which receives the output of op amp 140 at its
non-inverting input via a resistor 156. An adjustable resistor 158,
a fixed resistor 160, and a +15 volt source of potential provide a
reference voltage for the inverting input of op amp 153 which is
selected to provide the desired peak pattern limit, such as 1.01
times full speed. When the output of op amp 140 exceeds the
reference, indicating speed limiting is necessary, op amp 154
switches to a positive polarity and a diode 162 applies a positive
voltage to junction 130. This positive voltage makes junction 130
less negative, and the resistance of JFET 104 is reduced to allow
the necessary current to flow for limiting the pattern signal. The
affect on the speed pattern signal is such that the responding
elevator car approaches the maximum speed limit smoothly, without
overshoot thereof.
As further illustrated in FIG. 2, the teachings of the invention
may be applied to monitoring the actual car speed, and in response
thereto to introduce limiting into the speed pattern signal. The
actual speed of the elevator car in the exemplary embodiment is
represented by signal VI1. Signal VT1 has a polarity responsive to
car travel direction, and it is applied to a buffer and absolute
value function 114', which may be similar to that described
relative to function 114. The output of function 114' is applied to
a peak and approach limiting function 136', which may be similar to
function 136, and the output of this function is applied to a
comparator 152', which may be similar to comparator 152. The output
of comparator 152' is applied to junction 130 via a diode 164, with
this circuit having the same affect on JFET 104 as hereinbefore
described relative to the acceleration and maximum speed channels
which monitored the speed pattern signal VSP'.
In general, it is felt that monitoring the hereinbefore mentioned
parameters of the speed pattern signal provides completely adequate
monitoring and limiting of the speed pattern signal. If additional
monitoring is desirable relative to the actual car speed, it is
felt that it is only necessary to monitor the maximum value
thereof. If the actual car speed VT1 were to be processed in order
to provide acceleration limiting, the acceleration signal would be
difficult to stabilize. Further, since stabilization thereof would
be tied to system dynamics, it may present a possible failure mode
if this monitoring channel were to go into oscillation.
FIG. 3 is a graph which illustrates the functioning of the various
monitoring and limiting features of the invention, added one
feature at a time. Curve 170 illustrates an extreme malfunctioning
speed pattern signal VSP which varies from zero in steps, instead
of smoothly with the desired rate of change as it would in a normal
speed pattern. Further, the maximum value of the speed pattern VSP
in curve 170 is twice rated maximum speed, with rated maximum speed
being indicated for one travel direction by dotted line R1, and for
the other travel direction by dotted line R2.
Curve 172 simulates the response of the elevator car to the speed
pattern signal 170, without any monitoring and limiting, as taught
by the invention. The car speed overshoots the maximum speed
dictated by the pattern, with the overshoot being even greater in
response to pattern reversal.
Curve 174 simulates the response of the elevator car to the speed
pattern signal 170, with only the peak limiting feature being
applied. In other words, only the function 136 of FIG. 2 is
effective, and capacitor 144 and resistor 146 would be eliminated.
It will be noted that while the car speed is now limited to the
full rated speed, that the car speed overshoots the maximum rated
speed as it adjusts to this limitation.
Curve 176 simulates the response of the elevator car to the speed
pattern signal 170 with peak limiting and exponential approach to
full speed. In other words, only function 136 of FIG. 2 is
effective, and capacitor 144 and resistor 146 would also be
connected into the circuit as illustrated. It will be noted that
the car speed approaches full speed smoothly and without overshoot
in response to a step increase in the pattern from zero to
full-speed, but some overshoot occurs in response to a step
reversal of the pattern.
Curve 178 simulates the response of the elevator car to the speed
pattern signal with peak limiting, exponential approach to full
speed, and acceleration limiting applied. In other words, functions
122 and 136 of FIG. 2 are both active. It will be noted that the
acceleration is limited, but no limiting is applied to pattern
failures, i.e., a step from full speed to zero, or to pattern
reversal, i.e., a step from maximum speed in one direction to
maximum speed in the other direction.
Curve 180 simulates the response of the elevator car to the speed
pattern signal 170 with peak limiting, exponential approach to
maximum speed, acceleration limiting, and slope limiting. In other
words, functions 122, 136 and 58 of FIG. 2 are all active. It will
be noted that pattern failure and pattern reversal, as well as step
increases, are all handled without exceeding maximum speed, without
any overshoot of maximum speed, and without exceeding desired
acceleration or deceleration rates.
* * * * *